1. Field of the Invention
This invention relates to an injection mold, and more particularly to an injection mold having a valve gate system.
2. Description of the Prior Art
There has been known a hot-runner injection mold having a valve gate system in which a valve pin is moved through a runner into and away from a gate to open and close the gate. The valve pin is inserted into the gate to close it after each injection stroke and the end face of the valve pin defines a part of the surface of an injection-molded article when the valve pin is in the gate.
The hot-runner injection mold having the valve gate system is advantageous over other hot-runner injection molds in that the opening area of the gate during the injection stroke can be large, and accordingly, flowability of resin is better, cycle time can be shortened and a thin article can be molded. Further since the gate is closed after the injection stroke, degating during mold opening stroke is facilitated.
However, since the valve pin is in the runner and is surrounded by hot resin, the gate part of the article opposed to the end face of the valve pin is less apt to cool and accordingly sinkmark is produced in the gate part, which deteriorates the appearance of the molded article.